Balance wheel assembly of a battery-driven timepiece

ABSTRACT

This invention concerns with a drive balance wheel assembly for use in an electronic timepiece, an impulse pin being fixedly mounted to steppingly drive an escape wheel. This improvement comprises the arrangement of said impulse pin so as to have an offset angle, 20* or more, relative to the common diameter of the balance and escape wheels for compensating unavoidable amplitude reduction as met with consumption of a source battery fitted in the timepiece.

United States Patent Kanazawa et al.

BALANCE WHEEL ASSEMBLY OF A BATTERY-DRIVEN TIMEPIECE Inventors: KozaburoKanazawa; Eiji Kawakami, both of Tokorozawa. Japan Assignee: CitizenWatch Co. Ltd., Tokyo,

Japan Filed: Sept. 28, 1970 Appl. No.: 76,122

Foreign Application Priority Data Sept. 29, 1969 Japan ..44/77676 US. Cl..58/28 D, 58/117, 74/1.5 Int. Cl. G04c 3/04, G04b 15/ 14, F 16h fieldof Search.....58/28, 28 A, 28 B, 28 D, 107,

is] 3,681,915 [4 1 Aug. 8, 1972 [56] References Cited UNITED STATESPATENTS 3,058,293 10/1962 Egger ..58/28 D Primary Examiner-Stephen J.Tomsky Assistant Examiner-Edith C. Simmons Jackson Attorney-Sughrue,Rothwell, Mion, Zinn & Macpeak ABSTRACT This invention concerns with adrive balance wheel assembly for use in an electronic timepiece, animpulse pin being fixedly mounted to steppingly drive an escape wheel.

This improvement comprises the arrangement of said impulse pin so as tohave an offset angle, 20 or more, relative to the common diameter of thebalance and escape wheels for compensating unavoidable amplitudereduction as met with consumption of a source battery fitted in thetimepiece.

2 Claims, 6 Drawing Figures PATENTE DAUG 8l972 3.681.915

SHEET 2 BF 2 SEC/ DAY DAILY ERROR SEC/ DAILY ERROR L6 L3 BATTERY VOLTAGEDAY} F l G. 6

I. 6 BATTERY VOLTAGE BALANCE WHEEL ASSEMBLY OF A BATTERY- DRIVENTIMEPIECE This invention relates to improvements in and relating to abalance wheel for use in a battery-driven electronic timepiece, whereinan impulse pin mounted on the balance wheel drives an escape wheel.

It is commonly known that the drive battery used in an electronictimepiece will be subjected to gradual voltage reduction as it consumesits power during extended use of the timepiece.

With reduction of the applying voltage thus caused, the operatingamplitude of the balance wheel will naturally be subjected to acorresponding gradual reduction, resulting in a corresponding alterationin the regular stepping movement of the timepiece.

In order to overcome such a conventional drawback of balance wheelamplitude reduction, a certain brake means is additionally fitted to themechanism at the cost of an increased power consumption.

As an alternative way, the hair spring is controlled in its windingangle which results, however, in considerable additional time and costin the timepiece manufacture.

As a still further counter measure, a provision of magnetic brake meansis made in close proximity of the balance wheel, so as to perform asimilar job for improving the isochronism of the timepiece.

TI-Ie main object of the invention is to provide an improved balancewheel, capable of providing a highly stabilized isochronism in theoperation of the timepiece fitted therewith, even when the balance wheelis subjected to amplitude variation caused by the battery consumption inthe above-mentioned sense.

In order to fulfill the aforementioned object, the drive balance wheelaccording to this invention is so designed and arranged that the impulsepin fixedly mounted on the wheel for driving an escape wheel ispositioned so as to establish a central angle of 20 or more on thebalance wheel as measured from the common diameter to the said bothwheels and with the balance wheel kept at its neutral position.

These and further objects, features and advantages of the invention willbecome more apparent when read the following detailed description of theinvention by reference to the accompanying drawings illustrative ofsubstantially a preferred embodiment of the invention.

In the drawings:

FIG. 1 is an axial sectional view of a preferred embodiment of the drivebalance wheel according to the invention wherein, however, the drivenescape wheel is also shown.

FIG. 2 is an enlarged schematic plan view of a conventional roller of abalance wheel, an impulse pin fixedly mounted thereon and a drivenescape wheel, shown in such position of the balance wheel which is heldin its stationary or neutral position.

FIG. 3 is a similar view to FIG. 2, showing the improved structureaccording to this invention.

FIG. 4 is a rather specific and still further enlarged plan view of amodified shape of a drive balance wheel embodying the principles of theinvention, wherein the driven escape wheel, sensing and drivingpermanent magnets mounted on the balance wheel and a stationary coilassembly adapted for cooperation with these permanent magnets are shownadditionally.

FIGS. 5 and 6 are isochronic performance curves of a drive balance wheelaccording to this invention.

Referring now to FIG. 1 of the accompanying drawings, numeral 10 denotesa balance wheel arbor which is rotatably mounted with its both ends byconventional timepiece plate 20 and a conventional balance bridge 21which are shown only partially on account of their very popularity andfor simplicity of the drawing. A pair of balance wheel discs 11a and 11bare fixedly attached at their centers to the arbor 10 and carry thereona plurality of permanent magnets 12a and 12b and counter weights 13a and13b, said magnets being arranged to electromagnetically cooperate with astationary coil means 14 which is fixedly mounted on the plate 20through a mounting means 15. Although not shown, the coil means 14consists of a sensing coil element and a drive coil element which arecompoundly wound into a single coil mass. These coil means 14 andmounting means 15 are shown in chain dotted lines and substantially bytheir respective outlines only for simplicity. The said coil elementsare connected electrically with a conventional electronic drive circuit,not shown, and a battery, again not shown, for transmitting sensedelectric signals to and receiving drive currents from the electroniccircuits when the balance wheel is kept in its oscillatory movement, aswill bemore fully described hereinafter. The balance wheel is providedwith a conventional hair spring 16 with its ends fixedly attached toconventional stud 17 and collet 18.

In close proximity to the lower end of the arbor 10,

.the latter is fixedly attached with a mounting disc 19 which mountsfixedly in turn an impulse pin 22.

An escape wheel 23 having peripheral ratchet teeth 23a is rotatablymounted by its arbor 25 between a second bridge 24, only partiallyshown, and the plate 20, said teeth being positioned in the acting areaof the impulse pin 22 when the escape wheel 23 rotates.

The escape arbor 25 is formed with an escape pinion 26 which isoperatively connected with a conventional movement gear train, fordriving the latter, although not shown.

A positioner magnet 27 for the escape teeth 23a is mounted fixedly onthe plate 20.

The centers of the balance wheel and thus the balance wheel arbor l0 andthe escape shaft 25 are denoted in FIGS. 2 and 3 at O and 0respectively; the common diameter connecting these centers is shown by achain-dotted line 28, respectively.

When the balance wheel is kept stationary and in its neutral positionillustrated by way of example in FIGS. 2 and 3 for the case of theconventional and the inventive arrangement, respectively, the impulsepin 22 will occupy the position on the common diameter in theconventional case and at certain angularly offset position relative tothe latter. According to our practical experiments, this offset anglealpha should be 20 or larger.

As was referred to hereinbefore, the electronic timepiece of the abovekind employing the escape wheel, the balance wheel amplitude will besubjected to a gradual reduction with reduction of the battery voltage,and this kind of amplitude reduction will naturally and adversely affectupon the isochronic performance of the timepiece. The thus causedisochronic error depends upon various factors such as escape error,winding angle of hair spring, eccentric mounting of the latter, shift ofthe center of gravity, and the like.

According to the prior technique, these erroneous factors have beenattempted to be remedied independently and separately. However, it isnaturally impossible to realize a complete compensation of these variousfactors as a whole, thus remaining always a certain degree of residualerror which will appear as the isochronic error making the timepieceperformance correspondingly inferior.

According to the present invention, the escape error which constitutes amain error of these various errors is so advantageously controlled thatall the remaining errors may substantially be cancelled out.

By mounting the impulse pin in an angularly offset position by a certainangle alpha, as measured at the neutral position of the balance wheelrelative to the escape wheel, as was specifically referred tohereinbefore, the escape error will increase gradually for a certainconstant amplitude of the balance wheel oscillation, and the thusresulted error is, as ascertained by our practical experiments,intimately related with increase of the offset angle of the impulse pin.

On the other hand, any person skilled in the art may well recognize thatthere is an exponential relationship between the balance wheel amplitudereduction in the above sense and the isochronic characteristic curve ofthe timepiece. According to our experimental knowledge, the escape errorcaused to appear in a latent sense in the arrangement according to thisinvention by the offset arrangement of the impulse pin takes always inthe shape of an exponential curve of substantially similar nature asbefore, yet in the opposite or compensating sense. This latent error canbe negative or positive, as the case may be, relative to the commondiameter to the both balance and escape wheels. Under conditionsaccording to the present invention the impulse pin is positively offsetfrom the the common diameter to that which has been shown and describedhereinabove.

By determining the isochronic curve for each commercialized timepiecemodel by experiments, a certain offset angle and its positive ornegative sign for the impulse pin can also be determined upon performingseveral minor experiments, so as to substantially cancel out the overallerror.

In this way, a highly favorable overall isochronic performancecharacteristic for a specific timepiece model can easily be provided.

FIGS. 5 and 6 represent isochronic error curves for the impulse pinmounted at nil and 20 of the offset angle as hinted in FIGS. 2 and 3,respectively, as being caused by the battery voltage variation.

The curve shown in FIG. 5 was obtained with the balance wheel arbor inits vertical position, while that shown in FIG. 6 was obtained with thearbor positioned in its horizontal position.

In the conventional arrangement shown in FIG. 2, the escape error wouldbe substantially nil by the provision of the impulse pin on the commondiameter.

The isochronic curves shown in FIGS. 5 and 6 represent each anappreciable inclination of change with gradual reduction of the sourcevoltage, representing in the mean (see K) a daily stepping error offigure, 0' represents again a standard deviation.

More specifically, since the escape arrangement shown in FIG. 2 has anegative isochronic characteristic curve as ascertained by practicalexperiments, it is necessary to a positive escape error for cancellingout the said negative error. Therefore, by positioning the impulse pin22 so as to have a clockwise offset angle relative to the commondiameter 28, the pin 22 will turn in the direction shown by the smallarrow and apply an impulse force onto one of the escape teeth 23a of theescape wheel at a position beyond the newly established neutral position29 of the balance wheel during the forward oscillation stroke of thelatter. During the reverse stroke of the impulse pin 22, it will applyan impulse force onto one of the escape teeth 23a at a position inadvance of the neutral position.

It should be noted that, in this case of the inventive escapearrangement, the escape wheel 23 will perform a certain return movement,not only in the forward oscillation stroke of the balance wheel shown bythe small solid arrow, but also in the reverse oscillation stroke of thesame wheel in the direction opposite to that, as shown by the dottedarrow. However, thanks to the positioning of a positioning magnet 27cooperative with one of the escape teeth 23a which is thus magneticallyattracted, the escape wheel 23 will be returned to the original positionupon performing said slight reverse movement. The drive force exerted bythe impulse pin 22 onto the escape teeth 23a in the forward directionshown by the arrow is selected to be larger than that applied by the pinin the reverse direction. Thus, with the offset angle of the impulse pinshown in FIG. 3, the applying force by the pin is larger than that whichwill be applied after passage of the pin through the neutral position29. This will result in the development of a positive escape error whichcan effectively compensate the aforementioned negative isochroniccharacteristic.

The initial rotational direction and the offset angle (alpha) of theimpulse pin 22 is determined based upon the isochronic characteristic asdetermined for the offset angle selected to nil. In practice, however,it will suffice to set the compensation for the case of the minimumusable source voltage such as, for instance, 1. 1 volts in the case ofFIGS. 5 and 6.

FIG. 4 illustrates a modification from that shown and describedhereinabove wherein modified balance wheels proper 11a (11b) are fixedlyattached to a balance arbor 10' and carry thereon permanent magnets 12a'(12b') and 12c (12d) adapted to electromagnetically cooperate with coilassembly 14. In diametral opposition to these permanent magnets, aunified and arcuated counter weight mass 13 is fixedly mounted on thebalance wheel. At the lower end part of the balance arbor 10', there isprovided an impulse pin 22' fixedly attached thereto as before. Thisimpulse pin 22 is also positioned with an offset angle amounting to 20or more, relative to the common diameter of the balance wheel and theescape wheel. Numeral 23' denotes the conventional escape wheel ofconventional design and having its arbor rotatably mounted as before,although not specifically shown, between the second bridge and thetimepiece plate as at 24 and 20 in the foregoing embodiment.

The same or similar constituent parts in the present modification areshown, irrespective of modified configuration thereof, by the respectivesame references as those employed in the foregoing so that no furtheranalysis would be necessary for better understanding of the presentmodification.

The functional mode of the modification is similar to that of theforegoing embodiment.

It will be clearly seen from the foregoing that according to the novelteachings of the invention, separate and independent removal ofoccational fluctuations of the winding angle of hair spring 16 and thereduction in battery voltage can be obtained by mounting the impulse pin22 of the mounting disc 19 at a positive angle relative to the commondiameter 28 between the escape wheel 23 and the mounting disc 19, whichwill cause an occasional alteration in the position of the center ofgravity which will influence the isochronic error of the drive balancewheel acting as the timebase of the above kind of battery-driventimepeice, can be substantially obviated.

With the balance wheel kept in its stationary or neutral position, inthe case of the timepiece according to this invention, the impulse pinis kept in no physical contact with the escape tooth, the balance wheelcan be started at the beginning stage of the balance wheel oscillationpractically under no load, thus providing a smooth and effectivestarting characteristic being attained without use of any mechanicalstarter means and capable of providing a favorable and ment of theoscillation amplitude.

The embodiments of the invention in which an excluisive property orprivilege is claimed are defined as folows:

l. In a drive balance wheel assembly for use in an electronic timepiecehaving an impulse pin fixedly mounted on the balance wheel arbor fordriving cooperation with an escape wheel, and a mounting plate forrotatably supporting said balance wheel arbor and escape wheel, theimprovement comprising said escape wheel having a plurality of ratchetteeth equally spaced around the outer periphery thereof, said ratchetteeth having two parallel radial edges, the outermost edge of eachradial tooth forming an acute angle with the edge of said tooth on theside in the direction of rotation of said escape wheel, said impulsewheel being formed as a rectangular pillar mounted perpendicularly onsaid balance wheel for engagement with said ratchet teeth in bothdirections of rotation of said balance wheel arbor, said impulse pinbeing positioned so as to establish a central angle of 20 or more on thebalance wheel as measured ahead of the common diameter to said bothwheels with the balance wheel kept at its neutral position, and apermanent magnet mounted on said plate between said plate and theratchet teeth of said escape wheel for cooperation with the planarsurface of each ratchet tooth to position said escape wheel as it isindexed by the engagement of said impulse pin it ea sais atc t 19am.

Th mizrw msntasslaimqqin C a 1, C terized by that said impulse pin ismounted fixedly on a mounting disc which is fixedly mounted in turn onthe arbor of said balance wheel.

repid develop-

1. In a drive balance wheel assembly for use in an electronic timepiecehaving an impulse pin fixedly mounted on the balance wheel arbor fordriving cooperation with an escape wheel, and a mounting plate forrotatably supporting said balance wheel arbor and escape wheel, theimprovement comprising said escape wheel having a plurality of ratchetteeth equally spaced around the outer periphery thereof, said ratchetteeth having two parallel radial edges, the outermost edge of eachradial tooth forming an acute angle with the edge of said tooth on theside in the direction of rotation of said escape wheel, said impulsewheel being formed as a rectangular pillar mounted perpendicularly onsaid balance wheel for engagement with said ratchet teeth in bothdirections of rotation of said balance wheel arbor, said impulse pinbeing positioned so as to establish a central angle of 20* or more onthe balance wheel as measured ahead of the common diameter to said bothwheels with the balance wheel kept at its neutral position, and apermanent magnet mounted on said plate between said plate and theratchet teeth of said escape wheel for cooperation with the planarsurface of each ratchet tooth to position said escape wheel as it isindexed by the engagement of said impulse pin with each of said ratchetteeth.
 2. The improvement as claimed in claim 1, characterized by thatsaid impulse pin is mounted fixedly on a mounting disc which is fixedlymounted in turn on the arbor of said balance wheel.